Small scale electron linear accelerators for industrial applications

The Neutron Physics group at Centro Atomico Bariloche (CNEA, Argentina) has evolved for more than forty five years around a small 25MeV linear electron accelerator. It constitutes our compact accelerator-driven neutron source (CANS), which is dedicated to the use and development of neutronic methods to tackle problems of basic sciences and technological applications. Its historical first commitment has been the determination of the total cross sections of materials as a function of neutron energy by means of transmission experiments for thermal and sub-thermal neutrons. This also allowed testing theoretical models for the generation of scattering kernels and cross sections. Through the years, our interests moved from classic pulsed neutron diffraction, which included the development of high-precision methods for the determination of very low hydrogen content in metals, towards deep inelastic neutron scattering (DINS), a powerful tool for the determination of atomic momentum distribution in condensed matter. More recently non-intrusive techniques aimed at the scanning of large cargo containers have started to be developed with our CANS, testing the capacity and limitations to detect special nuclear material and dangerous substances. Also, the ever-present “bremsstrahlung” radiation has been recognized and tested as a useful complement to instrumental neutron activation, as it permits to detect other nuclear species through high-energy photon activation. The facility is also used for graduate and undergraduate students’ experimental work within the frame of Instituto Balseiro Physics and Nuclear Engineering courses of study, and also MSc and PhD theses work.

An empirical model for small circular electron fields was developed. This can be of great help in the treatment planning process for small circular electron fields. A complete dosimetric analysis of the circular fields defined by electron cutouts diameters (2 cm–9 cm) was done for nominal electron energies ranging between 6 MeV and 20 MeV using a 3D water phantom and a pin-point ion chamber. Properties studied included depth dose, in-air inverse-square fall-off, and beam profiles. The Varian Clianc 2100 C accelerator was modelled, benchmarked and Monte Carlo simulations were performed using the EGSnrc/BEAMnrc code for the small circular cutouts. A simple exponential model was found to accurately predict the very important therapeutic depth (90% of Dmax) for the small circular field size within an accuracy of better than 2 mm in most cases. The model has only two parameters (d90 and ‘b’). Also, the penumbra widths (90% of the off-axis profiles) of these small circular electron fields were studied and least square fitted to a simple quadratic model. Full dosimetric profiles of these small circular electron fields were further studied using the benchmarked Monte Carlo simulations. This study presents a simple model to predict the very important therapeutic depth (90% of Dmax) and a recipe to develop such an electron treatment model for any linear accelerator system. Such predictions can be extremely valuable and time saving prior to treatment planning involving not only small circular shaped electron fields but also irregularly shaped electron fields.

It is proposed to use chromium-compensated semi-insulating GaAs detectors for detecting high-power nanosecond X-ray pulses. An X-ray facility based on a small direct-acting electron accelerator “Sinus-150” developed at the Institute of High-Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk was used as a source of pulsed X-ray radiation. The detectors are shown to detect 5 ns pulses under exposure to 30 mR radiation during one pulse without distortions. In so doing, one-ampere currents flow through the active detector area 0.2 cm2. It is found that the physical processes limiting the working capacity of GaAs detectors are due to capture of nonequilibrium electrons and holes by deep centers. At the nonequilibrium charge-carrier concentrations higher than 5·1013 cm3, nonuniform distributions of the electric field are formed in the active region and these can result in distortion of the output detector signal shape.

A simple electron beam switching pulse generator for small accelerators

We propose a Photon Storage Ring (PhSR), which is a novel free-electron laser (FEL) composed of a compact synchrotron radiation (SR) source and a cylindrical mirror surrounding the electron orbit. The SR source is an exactly circular type and the mirror is concentric to the electron orbit. In this scheme SR is reflected back tangentially to the electron orbit by the cylindrical mirror and interacts with the electrons, leading to the laser oscillation. The PhSR posesses many ideal features: since SR is confined by the mirror then all the radiations emitted at an angle to the electron orbit exibit good coherency; since the interaction occurs continiously along the electron orbit, a large gain is expected; and since all radiations are extracted through a simple opening, an extraction efficiency is fairly high. Compared with a conventional FEL, PhSR is capable of generating a high laser power by using a relatively small accelerator with a small electron beam current.

The parameters of radio radiation generated in an air medium by an electron beam from a RELUS-1 small electron accelerator (Radiation Acceleration Center, MIFI) were studied theoretically and experimentally. Theoretical models for the generation of electromagnetic fields over the frequency range 10–3000 MHz induced by an electron beam were developed and studied. Electromagnetic fields from a beam of electrons were recorded over the frequency ranges 140–160 and 2794–2804. The discrepancy between theoretical estimates and recorded values was less than 50%.

Proton Microprobes and Their Applications

GIS is widely used in the fields of high voltage, ultra-high voltage and ultra-high voltage. The structure of GIS is compact, the floor area is small, the configuration is flexible and the reliability is high. Moreover, it has strong security and strong environmental adaptability. However, the electric field strength in GIS is very strong, once there are some defects in the equipment, partial discharge will occur, resulting in insulation deterioration of GIS equipment. In this paper, positioning detection technology is used, A fast live detection method of power equipment in complex area based on lilac is proposed. The position of the discharge source is roughly located, and then the linear electron accelerator is used to accurately locate the partial discharge source, which improves the efficiency of defect location. Based on the linear electron accelerator, GIS signal detection device is studied. In the detection, it is necessary to obtain the data generated by partial discharge signal, high-frequency current data and data for comparative analysis, so as to effectively eliminate the interference signal in GIS field, and improve the accuracy and defect type identification.

Studies were made of the radial motion of a strongly relativistic electron in a linear accelerator with alternating-gradient focusing. (R.V.J.)

The overall objective of this project was to study the acceleration of electrons to very high energies over very short distances based on trapping slowly moving electrons in the fast moving potential wells of large amplitude plasma waves, which have relativistic phase velocities. These relativistic plasma waves, or wakefields, are the basis of table-top accelerators that have been shown to accelerate electrons to the same high energies as kilometer-length linear particle colliders operating using traditional decades-old acceleration techniques. The accelerating electrostatic fields of the relativistic plasma wave accelerators can be as large as GigaVolts/meter, and our goal was to study techniques for remotely measuring these large fields by injecting low energy probe electron beams across the plasma wave and measuring the beam’s deflection. Our method of study was via computer simulations, and these results suggested that the deflection of the probe electron beam was directly proportional to the amplitude of the plasma wave. This is the basis of a proposed diagnostic technique, and numerous studies were performed to determine the effects of changing the electron beam, plasma wave and laser beam parameters. Further simulation studies included copropagating laser beams with the relativistic plasma waves. New interesting results came out of these studies including the prediction that very small scale electron beam bunching occurs, and an anomalous line focusing of the electron beam occurs under certain conditions. These studies were summarized in the dissertation of a graduate student who obtained the Ph.D. in physics. This past research program has motivated ideas for further research to corroborate these results using particle-in-cell simulation tools which will help design a test-of-concept experiment in our laboratory and a scaled up version for testing at a major wakefield accelerator facility.

Observations of ionospheric modification by the Tromsø heating facility with the mobile diagnostic equipment of IZMIRAN

The recent interest in investigating photonuclear reactions near the threshold (at electron and photon energies below 10 MeV) requires electron beams with the improved properties. In this work, results are presented from studies conducted on the LUE-8-5RV linear electron accelerator at the Institute for Nuclear Research, Russian Academy of Sciences. These investigations allow the generation of an electron beam whose energies can be adjusted in the range of 4–10 MeV with energy resolution (FWHM) from 1% at currents of up to 6 μA and 10% at maximum currents of up to 300 μA with a repetition rate of 300 s−1 and a pulse width of 3 μs. High-resolution beams are obtained using a magnetic beam-forming system with beam deflection of 270°. A series of experiments on, e.g., exciting isomeric nuclei in the region of pygmy resonances and measuring electron-to-positron conversion near the threshold for a number of nuclei, are performed.

Active neutron interrogation is a nondestructive active method that consists in inducing fission reactions on actinides (e.g., <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">235</sup> U and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">239</sup> Pu) and then in detecting prompt and delayed particles emitted further to these reactions. This method is required in various application fields such as radiological characterization of nuclear waste packages and homeland security. Neutron sources traditionally used in neutron interrogation facilities are deuterium-tritium neutron generators. However, a linear electron accelerator (LINAC) can also be used as a photoneutron generator. When accelerating electrons with energy lower than 10 MeV, the use of a secondary target such as heavy water is of interest to convert bremsstrahlung photons to neutrons and to improve neutron production. In this paper, we characterize the photoneutron flux emitted by a Linatron-M9 VARIAN LINAC and the photoneutron flux emitted by a secondary target made of heavy water. We show that operating the LINAC at 9 MeV, the average emission intensity reaches 1.08 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> neutrons per second, which is on the order of 10× higher than the maximum average emission intensity delivered by a traditional deuterium-tritium neutron generator. Then, we carry out neutron interrogation measurements on uranium samples using the Linatron-M9 LINAC and a secondary target made of different volumes of heavy water. We show that prompt neutron signals were enhanced when using 16 kg of heavy water and operating the LINAC at 9 MeV. Performances of the setup were then assessed by carrying out measurements on a mockup of nuclear waste drum containing different types of matrices. Considering a 0.22-g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> iron matrix and a uranium sample at the center of the drum, 44 mg of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">235</sup> U can be detected in 5 min of irradiation time using a single detection block housing five 150NH100 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He detectors.

A compact 15.0-MeV, 1.5-kW electron linear accelerator (LINAC) was successfully constructed to provide an electron beam for the first photoneutron source at the Shanghai Institute of Applied Physics, Shanghai, China. This LINAC consists of five main parts: a thermal cathode grid-controlled electron gun, a pre-buncher, a variable-phase-velocity buncher, a light-speed accelerating structure, and a high-power transportation beamline. A digital feedforward radio frequency compensator is adopted to reduce the energy spread caused by the transient beam loading effect. Furthermore, a real-time electron gun emission feedback algorithm is used to keep the beam stable. After months of efforts, all the beam parameters successfully met the requirements of the facility. In this paper, the beam commissioning process and performance of the LINAC are presented.

A description is given of a small heavy-ion linear accelerator based on the use of a twin transmission line as first suggested by Sloan and Lawrence. Ions are accepted if their e/m values are ⅛ or greater (relative to the proton) and are accelerated to a final energy of 1.04 Mev/nucleon. The accelerator has 40 drift tubes fitted with focusing grids, and about 350 kw of pulsed rf are needed for ions of e/m=⅛. The radio frequency is 25 Mc, and the accelerator is pulsed at up to 50 pps with a pulse length of 500 μsec. Injection velocity is 0.007 c, corresponding to a dc acceleration from the ion source through 180 kv for an ion of e/m=⅛. Ions are produced in a pulsed dc arc of the Penning type operating in a magnetic field of 1000 gauss and the dc accelerating voltage is supplied by an electrostatic generator. Typical pulsed meter currents so far obtained are, for He+, input 4 ma, output 150 μa; for N2+, input 3 ma, output 75 μa. The accelerator is the first stage of three which will take the ions to a final energy of 10 Mev/nucleon. The second and third stages, which are under construction, will be cavity resonators of the Alvarez design.